<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <!-- 组选择器 以 , 分割开 公共的样式设置 可以使用组选择器 -->
    <style>
        .box1, .box2, .box3{
            width: 100px;
            height: 100px;
        }

        .box1{
            background: red;
        }

        .box2{
            background: blue;
        }

        .box3{
            background: green;
        }

    </style>
</head>
<body>
<div class="box1"></div>
<div class="box2"></div>
<div class="box3"></div>
</body>
</html>